1. Field of the Invention
The present invention relates to an ink jet recording apparatus and its ink jet recording head, and more particularly to an ink jet recording apparatus which has a full-line type ink jet recording head having a recording area covering one line of a recording medium to be fed in a feeding direction substantially perpendicular to the line and to an ink jet recording head assembly.
2. Description of the Prior Art
Conventionally, as known to be an ink jet recording head used for an ink jet recording apparatus, there are two types of ink jet recording heads; a serial type of ink jet recording head which records information on a recording medium such as a recording sheet by moving its single head assembly perpendicularly to the feeding direction of the recording sheet and a full-line type of ink jet recording head. In the latter type, an ink jet recording head assembly is constructed in the form of a one dimensional array of ink jet discharging orifices covering the substantially full range of recording columns on a recording sheet and each ink jet discharging orifice is linked to an ink jet energy generation device via a liquid passage both of which are also arranged behind the ink jet discharging orifice. In view of the recording efficiency, a full-line type ink jet recording head is more advantageous than a serial type.
FIG. 6 shows an illustrative example of a full-line type ink jet recording head. In FIG. 6, a component 1 is a first plate or a substrate on the surface 1A of which a plurality of ink discharging orifices 2 are arranged with a close pitch and a high density, and furthermore, liquid passages not shown in FIG. 6; are formed on the substrate 1 and are connected to the ink discharging orifices 2, and electro-thermal converting elements used as ink jet energy generation devices and so on. And components 3A and 3B are ink supply tubes supplying ink into a recording head 10, and component 4 is a second plate or a base plate for supporting fixedly the substrate 1. The substrate 1 and the base plate 4 are glued firmly together in an ordinary case by adhesive materials .
So far, the recording head 10 made as described above is mounted in a recording apparatus with its position fixed precisely at an appropriate place. Ink is supplied through ink supply tubes 3A and 3B from an ink supply means not shown in the figure. The recordings are made by making use of thermal energy generated by driving the electro-thermal converting elements used as ink jet energy generating devices in accordance with input recording signals, discharging ink droplets from the ink discharging orifices 2 and then landing the droplets on the surface of a recording sheet which is placed against the discharging orifices 2. And also, for example, by placing four recording heads 10 described above in parallel with one another and by ejecting ink with different colors from each of recording heads, respectively, that is, colors of cyan, yellow, magenta and black, it is possible to establish full-color recording.
In the conventional full-line type of recording heads as described above, however, the length of a recording head in the longitudinal direction is required to get longer as the width of recording sheets get wider, and at the same time, the length of a recording head in the latitudinal direction tends to be taken shorter because a main wafer is sliced into a number of pieces used as a plurality of substrates in view of fabrication and production efficiency. As a result, as shown in FIG. 8B and FIG. 8C, inevitably, the amount of warp of a recording head in the longitudinal direct ion has a tendency to be larger.
In order to reduce the amount of warp, when bonding the first plate or the substrate 1 and the second plate or the base plate 4, in general, the substrate 1 is reinforced by an external force and glued firmly onto the base plate 4 so that the warp in the substrate 1 may be compensated. In many cases, the longer the substrate 1 is in the longitudinal direction, the more difficult and incomplete is the compensation of the warp.
In particular, in the case of making full-color recording by placing a plurality of full-line type recording heads in parallel with one another and by ejecting ink with different colors from each of the recording heads and trying multiple print on the same column spot, due to deviated warp in each recording head, landing positions of ink droplets from ink jet discharging orifices of different recording heads on the same column are not identical on the surface of a recording sheet. As a result, for example, as shown in FIG. 7B, due to a mismatch of landing positions of ink droplets with different colors onto a recording sheet such as so-called color deviations, complex color tones mixed with several color tones each corresponding to an individual recording head can not be reproduced completely. In particular, as shown in FIG. 8B and FIG. 8C, in the case that any pair of recording heads each having warp in opposite directions with respect to each other are mounted in an ink jet recording apparatus, when driving the pair of recording heads and trying perform multiple print on the same line with these recording heads, at the columns at opposite line ends of an array of discharging orifices 2, that is, at the columns on the right and left sides of a recording sheet, ink droplets from both recording heads can be directed exactly to an identical position on the sheet. On the other hand, under the same condition as that described above, in trying multiple print in the neighbor of the central portion of the recording sheet, colored ink droplets can not be directed to an identical position on the recording sheet as shown in FIG. 7B.
As described above, in recording information on a recording sheet by mounting a full-line type recording head having a warp into a recording apparatus, it is difficult to record an exact straight line on the recording sheet. And furthermore, in particular to conventional apparatuses, making use of a plurality of recording heads, each head corresponding to a single ink color, for trying to direct multiple colored ink droplets onto an identical position for full color printing, landing positions of ejected ink droplets on the recording sheet are deviated from a straight line due to warp of the recording head. Especially in the area of the central portion of the recording sheet, it is much more difficult to obtain an exact and uniform matching of landing positions of ink droplets with different colors on the recording sheet. Hence, there was such a disadvantage in the conventional ink jet recording apparatus that complex color tones given by mixing several single color tones are different in positions on the recording sheet and the quality of print was reduced.